The present invention relates in general to motion picture projectors of the slot-loading type having a projection slot, and more particularly to improvements in the housing thereof including the film threading assembly for the projection slot for greater ease and reliability of threading, biasing, and maintaining the motion picture film in proper alignment for projection within the projection slot.
In the prior art, users of motion picture film projectors have frequently experienced difficulty in threading the film into the motion picture projector. Part of the difficulty has arisen because of the long and circuitous threading route which has been typical of such prior art manual threading systems. In such systems, it has been generally necessary to thread the film manually around a number of toothed sprockets, through the film shuttle and around a sound drum, while placing the perforations in the film in mesh with the teeth of the appropriate sprocket, while enclosing the guide members and while holding the film in contact with the sprockets. It has also been necessary to manually establish loops of the correct lengths between the drive sprockets on either side of the film shuttle intermittent advance mechanism.
In practice, it sometimes is found that threading of the film in a projector of this type is a complicated and difficult operation. If the film is threaded incorrectly, it is likely to be damaged and to cause unsatisfactory performance of the projector.
In order to overcome this and other difficulties associated with manual threading of the film, many "self-threading" projectors have been proposed, some of which have been commercially produced. In such a "self-threading" projector, the end of the film is generally introduced endwise into a slot, which then directs the film end to a first toothed sprocket, which sprocket hopefully engages the film perforations and drives the film forward when the mechanism is in motion. The end of the film strip is then guided by a series of curved members which force it to travel in succession to another part of the film drive system, where the film end is engaged successively by various other driving members and sprockets. When the leading end of the film has been carried through a complete threading path, the film emerges from the mechanism and is attached to a takeup reel.
These "self-threading" projectors have alleviated some of the difficulties found in manual threading projectors, but have nonetheless displayed several residual and new disadvantages. In view of such disadvantages, the slot loading projector has been developed. In one such slot loading projector, such as is shown in U.S. Pat. No. 3,259,291 to Maurer, for example, the housing thereof includes a slot for confining and containing the film during projection thereof. The opposite ends of such projection slot have stationary film guide members, which may be in the form of an inclined surface, such as a truncated cone or may include larger extended edge portions, such as for example ridges. In either case, the surface of the film guide member is inclined such that a strand of film placed around either guide member and subjected to a slightly endwise tension will slide laterally and downwardly in the direction of the slant of the guide member into the slot for projection.
While the above stationary slot loading mechanism has been functional in general, improvements in the reliability and functioning thereof are deemed desirable.